A. Field of the Invention
The present invention relates to a clutch cover assembly to disengage a clutch disk from a flywheel.
B. Description of Related Art
In general, a clutch cover assembly, which is used in, for instance, automobile clutches, includes a pressure plate which presses a friction facing of a clutch disk against a flywheel of an engine. The clutch cover assembly usually includes a clutch cover which surrounds and supports the pressure plate, and a diaphragm spring which biases the pressure plate into engagement with the friction facing of the clutch disk.
A outer circumferential part of the clutch cover is typically bolted or attached in some way to an outer circumferential portion of the flywheel. The pressure plate is coupled to the clutch cover by a coupling mechanism in a manner such that relative rotation between the pressure plate and the clutch cover is restricted but limited axial movement of the pressure plate is possible.
A plurality of coupling mechanisms described above are positioned at spaced apart intervals in a circumferential direction along the outer circumferential portion of the clutch cover assembly. Typically, each mechanism is composed of a strap plate which extends in a direction tangent to an outer periphery of the clutch cover. The strap plate is made of an elongated plate-like elastic body, one end being attached to the clutch cover and the other end being attached to the pressure plate. By this mechanism, the pressure plate can rotate together with the clutch cover. For ideal function and positioning of the strap plates, openings are formed at the outer circumferential portions of the clutch cover to accommodate the strap plates.
For ideal operation, each of the strap plates must couple the clutch cover to the pressure plate in a circular direction as described above, but also, when disengaging the clutch, must bias the pressure plate away from engagement with the friction facing of the clutch disk. Therefore, each of the strap plates must have a predetermined circumferential length, with respect to the pressure plate and clutch cover, to provide adequate biasing force.
One problem with strap plates as currently used in the art is that the openings in the clutch cover that accommodate the strap plates must have a relatively large circumferential length in order to correspond to the relative length of the strap plate. As the result, the clutch cover may be weakened due to the discontinuities associated with the openings. The clutch cover, in some applications, may develop cracks or undergo slight deformation due in part to centrifugal forces.
In addition, the clutch cover provides a annular fulcrum about which the diaphragm spring pivots. There is a possibility that, due to its insufficient strength, the clutch cover may undergo slight deformation resulting in mis-alignment of the position of the fulcrum. Therefore, the performance of the clutch during engagement and disengagement may be diminished.
On the other hand, when a strap plate having a short circumferential length is used, the circumferential length of the opening may be reduced thus improving the strength of the clutch cover. However, in this case, the shorter strap plate has a greater possibility of undergoing significant deformation and bending and the pressure plate moves back and forth between engagement and dis-engagement with the friction surface of the clutch disc. Therefore, the shorter strap plate may prematurely wear as a result of fatigue.